Management of extent migration on tiered storage

ABSTRACT

Aspects of the present disclosure are directed toward a method, a system, and a computer program product for managing the migration of extents on tiered systems. The method can include receiving a space reservation request for one or more requested extents on a first storage tier of a storage system. The method can also include releasing a first storage tier reserve space that includes one or more first tier reserved extents in response to the first storage tier reserve space being insufficient for the reservation request. The method can also include migrating the one or more requested extents to the first storage tier reserve space.

BACKGROUND

The present disclosure relates to data storage systems, and morespecifically, to migrating data within data storage systems.

A data storage system can have one or more storage tiers in one or morestorage devices. Tiered storage is a data storage environment consistingof two or more kinds of storage delineated by differences in at leastone of these four attributes: price, performance, capacity and function.Any significant difference in one or more of the four definingattributes can be sufficient to justify a separate storage tier.

Extents can be managed on tiered storage. An extent is a contiguous areaof storage in a computer file system, reserved for a file. When aprocess creates a file, file-system management software allocates awhole extent. When writing to the file again, possibly after doing otherwrite operations, the data continues where the previous write left off.This can reduce or eliminate file fragmentation and possibly filescattering too. An extent-based file system (i.e., one that addressesstorage via extents rather than in single blocks) need not requirelimiting each file to a single, contiguous extent.

SUMMARY

Embodiments of the disclosure can include a method, a system, and acomputer program product for managing extent migration on tiered storagedevices.

An aspect of the present disclosure is directed toward a method. Themethod can include receiving a space reservation request for one or morerequested extents on a first storage tier of a storage system. Themethod can also include releasing a first storage tier reserve spacethat includes one or more first tier reserved extents in response to thefirst storage tier reserve space being insufficient for the reservationrequest. The method can also include the migration of one or morerequested extents to the first storage tier reserve space. The releaseof the first storage tier reserve space can occur by prioritizing aplurality of extents on the first storage tier. The release can alsooccur by determining a space deficiency for the space reservationrequest in the first storage tier. The release can also occur byselecting one or more migrating extents on the first storage tier thatare at least equal to the space deficiency. The release can also occurduring the migration of one or more migrating extents to a secondstorage tier in response to the second storage tier having a secondstorage tier reserve space for the one or more migrating extents.

Another aspect of the present disclosure is directed toward a system.The system can include a plurality of storage tiers on one or morestorage devices with at least one high performance storage tier relativeto the plurality of storage tiers, wherein the storage tier has one ormore extents. The system can include a prioritization module configuredto determine a priority of an extent on the plurality of storage tiersand communicate the priority to a space reservation manager. The systemcan include the space reservation manager. The space reservation managercan be configured to receive a space reservation request for a migrationof a requested extent to a first storage tier. The space reservationmanager can be configured to release, in response to one or moreavailable extents on the first storage tier being insufficient for thespace reservation request, a first storage tier reserve space. Therelease can occur by receiving the priority of a plurality of extents onthe first storage tier from the prioritization module. The release canoccur by determining a space deficiency between the one or morerequested extents for the space reservation request and the one or moreavailable extents in the first storage tier. The release can occur byselecting one or more migrating extents from the plurality of extents onthe first storage tier that are at least equal to the space deficiency.The release can also occur by migrating the one or more migratingextents to a second storage tier in response to the second storage tierhaving sufficient space for the one or more migrating extents. The spacereservation manager can be configured to migrate the one or morerequested extents to the reserve space on the first storage tier.

Yet another aspect is directed toward a computer program product.

The above summary is not intended to describe each illustratedembodiment or every implementation of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings included in the present application are incorporated into,and form part of, the specification. They illustrate embodiments of thepresent disclosure and, along with the description, serve to explain theprinciples of the disclosure. The drawings are only illustrative ofcertain embodiments and do not limit the disclosure.

FIG. 1 illustrates a block diagram of a storage system that limitsaccess for migrations across storage tiers, according to variousembodiments.

FIG. 2 illustrates a block diagram of a storage system that managesextents having different priorities, according to various embodiments.

FIG. 3 illustrates a block diagram of a migration in a storage systemwith three tiers, according to various embodiments.

FIG. 4 illustrates a flowchart of a method of migrating extents torelease reserve space on a storage system, according to variousembodiments.

FIG. 5 illustrates a flow chart of a method to release reserve space ona target tier, according to various embodiments.

FIG. 6 illustrates a flowchart of a method of migrating a low priorityextent to a higher-level tier than the target tier, according to variousembodiments.

FIG. 7 illustrates a block diagram of a prioritization system that canbe used in the prioritization module, according to various embodiments.

FIG. 8 depicts a block diagram of automated computing machinery,according to an embodiment.

The descriptions of the various embodiments of the present disclosurehave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein

DETAILED DESCRIPTION

Aspects of the present disclosure relate to management of extents ontiered storage, more particular aspects relate to a space reservationmanager (SRM) that receives a request to migrate an extent to a targettier. If there is not any reserve space in the target tier, then thespace reservation manager can release space in the target tier bymigrating low priority, or cold extents away from the target tier (e.g.,a higher or lower performance tier) to release reserve space on thetarget tier. While the present disclosure is not necessarily limited tosuch applications, various aspects of the disclosure may be appreciatedthrough a discussion of various examples using this context. The termcold extent can be used to refer to a specific type of low priorityextent and can be used interchangeably throughout this disclosure.

In tiered storage, the individual tiers in the storage system may bemanaged by a storage controller. The individual tier may have one ormore ranks within the tier to assist in managing the extents within thetier. For example, extents assigned to a rank may be promoted anddemoted based on extent performance.

Storage systems, such as IBM® Easy Tier ®, can require that eachcomponent requests a space reservation for itself. The space reservationcan be for an extent. A consistent mechanism or central service mayexist. For example, in Easy Tier ®, a component can record how manyextents to reserve for each tier by storage pool. Then, Easy Tier® canpoll the various components to see if there is available space. EasyTier® can query an Easy Tier® Application's records and then triggerspace reservation accordingly. Easy Tier® queries all other components.

In various embodiments, a target tier for the space reservation can berequested. If there is not any available or accessible space on therequested target tier, then the storage system can perform a number ofactions. For example, the storage system can move related extentsthrough WARM DEMOTE which moves hot extents from the target tier to alower tier. However, a number of problems can develop when hot extentsmigrate to the lower tier, the hot extents may overload the lowerstorage tier. The overloading can lead to performance issues. Moreover,some current space-reserving policies may not support the downwardmigration of hot extents from the lowest tier in a pool, since therewould be no lower tier than the lowest tier.

In various embodiments of the disclosure, an SRM can exist that migratesextents, such as cold extents, away from the target tier and to anothertier, such as a higher tier, which can improve durability of the highertier.

FIG. 1 illustrates a block diagram of a storage system 100 that limitsaccess for migrations across storage tiers, according to variousembodiments. The storage system 100 can have one or more storagedevices. Each storage device can have one or more tiers and each tiercan have one or more ranks. The storage tiers can have differentperformance levels. For example, one storage tier can have a higherrelative performance than another storage tier which can be measuredusing performance metrics such as access times, or access frequencies.

The storage system 100 illustrates the reserved space for various extentmanagement activities. The storage system 100 can utilize accessiblespace and reserved space. The accessible space is space made availablefor any storage activity while the reserved space can be made accessiblefor specific storage activities. The reserved space can also includefree space within the storage system for the specific activity. Forexample, for an extent migration to a storage tier, the reserve spacecan be made accessible to the extent for the purposes of the migration.There may be more free space on the storage system, but not for thepurposes of migration. The reserved space can also be a space availableto an extent.

As shown, the storage system 100 can include a Space Reservation Manager(SRM) 110 to coordinate the migrations from an upper tier 112 and to alower tier 114. For example, the space reservation manager 110 canreceive an instruction from the upper tier 112 and transmit furtherinstructions to the lower tier 114. The SRM 110 can be a set ofinstructions or a module on a storage controller for multiple drives.

The upper tier 112 can have one or more extents, e.g., extent 116, andextent 118. In various embodiments, the upper tier 112 can be a fastaccess storage device, or high performance drive, such as a Solid StateDrive (SSD) or a faster access drive compared to the lower tier 114. Theupper tier 112 can request to demote the extent 118, or swap the extent116. Other extent management actions are contemplated including promote,or a cascading migration. The request can be made to the SRM 110.

In various embodiments, the SRM 110 can receive the request to demoteextent 118 from the upper tier 112. The SRM 110 will search for reservespace on the lower tier 114 that is sufficient to store the extent 118.For the demote operation of extent 118. The SRM may only be allowed readaccess or visibility to certain extents. In various embodiments, the SRMcan be allowed read access for certain blocks on a storage device.

The lower tier 114 can have the extents 120, 122, 124, and 126. Extents122 and 124 can be visible to the SRM 110 in all circumstances. Extents120 and 126 can be considered reserve space depending on the function.For example, the SRM 110 can view extent 126, but not extent 120, asavailable for the extent 118 demotion. Assuming that all extents in thesystem 100 are of equal size, the SRM 110 can prioritize extent 122 overextent 126. If the extents are of unequal size, and extent 118 is largerthan extent 122, then the SRM 110 can migrate extent 118 to both extent122 and extent 126. If an extent is not available due to the extentbeing used, then the extent may be invisible or unavailable to the SRM110.

In various embodiments, a swap operation can occur. The swap operationcan reserve space on a lower tier so that a swap between two extents canoccur without being stuck. A swap operation can replace an extent fromthe upper tier, e.g., extent 116, with an extent from the lower tier114. The swap operation can create free space on a tier that may nothave been originally available. For example, the migration of the extent116 to the lower tier 114 and the corresponding migration of anotherextent from the lower tier 114 to the upper tier 112, can free up spaceon the lower tier 114 if the extent from the lower tier 114 is smallerthan the extent 116. Furthermore, the swap operation can allow a coldextent from the upper tier 112 to migrate to the lower tier even thoughthere is not the necessary accessible space in the lower tier 114. Invarious embodiments, the SRM 110 can identify the extent 120 to swapwith extent 116. The extent 116 can be first moved to the lower tier 114into the accessible extent 124. Then, the extent 120 can be migrated tothe upper tier 112.

FIG. 2 illustrates a block diagram of a storage system 200 that managesextents having different priorities, according to various embodiments.The storage system 200 can have a space reservation manager 214 thatincludes a prioritization module 216. The SRM 214 can be refer to theSRM used throughout this application. The space reservation manager 214can manage a space reservation request from multiple tiers, e.g., tierone 210 and tier two 212. Although two tiers are shown in the storagesystem, more than two storage tiers in a storage system 200 arecontemplated. The tiers in the storage system can originate from asingle drive or partition. In various embodiments, the tiers can bereferred to as storage tiers and can also refer to different rankswithin a particular tier.

According to various embodiments, the space reservation manager 214 canmonitor tier one 210 for an extent with an appropriate priority. Tierone 210, as illustrated, contains three areas: a space with a highpriority extent 218, a reserve space 220 that is inaccessible to the SRM214, and a reserve space 222 that is accessible to the SRM 214. The highpriority extent 218 can have the appropriate priority to migrate to alower tier. For example, the high priority extent 218 can be a hotextent, i.e., a frequently accessed extent, that degrades theperformance, e.g., access times, of tier one 210. The prioritizationmodule 216 can assign a high priority to the extent for migration to alower tier, e.g. tier two 212, which can reduce the hotness on thehigher tier.

Tier two 212, as illustrated, can have three areas: a reserved area 224that is accessible to the SRM 214, an area containing a low priorityextent 226, and a reserved extent 228 not accessible to the SRM 214. TheSRM 214 can receive a request a migration for the high priority extentto tier two 212. If the reserved space 224 does not have sufficientspace to accommodate the high priority extent 218, then the SRM 214 candecide to swap the low priority extent 226 of tier two 212 for the highpriority extent 218 of tier one 210. The SRM 214 can promote the lowpriority extent 226 to the reserved space 222. Once promoted into thereserve space 222, the high priority extent can be warm demoted into thespace formerly occupied by the low priority extent 226 and the reservespace 224.

The warm demote can be an operation whereby a hot extent is demoted intoa lower tier to improve the performance of the higher tier. In variousembodiments, the high priority extent 218 can be demoted into thereserve space 224 and then the low priority extent 226 can be promotedinto the reserved space 222.

FIG. 3 illustrates a block diagram of a migration in a storage system300 with three tiers, according to various embodiments. Although numbersare used to show a particular order in the storage system 300, thevarious operations may be conducted in any order. The storage system 300can have three tiers: tier 0, tier 1, and tier 2. The tiers can bearranged by performance. For example, tier 0 can have the fastestrelative access time such as a solid state disk (SSD), tier 1 can be anenterprise (ENT) drive, and tier 2 can have the slowest relative accesstimes such as a serial advanced technology attachment (SATA) drive. Invarious embodiments, the tiers can refer to ranks within a tier or tierson the same drive.

The storage system 300 can have a storage controller 310. The storagecontroller 310 can include a space reservation manager 312 and aprioritization module. In various embodiments, the SRM 312 can beseparate from the storage controller 310. The SRM 312 can identify anextent M for migration to tier 1. Extent M can come from various tiersin the storage system including other tiers not pictured. In variousembodiments, extent M can be selected from a higher tier similar to thestorage system 200 in FIG. 2. Extent M can also come from an externalsource to be copied onto the storage system 300.

Tier 1, i.e., the target tier, can have one or more extents, e.g.,extent A, extent B, extent C. The storage controller 310 can send amigration request to tier 1 for extent M. If there is insufficient spaceto accommodate extent M, the storage controller 310 can request to thespace reservation manager 312 for more space.

The space reservation manager 312 can prioritize the extents existing intier 1, e.g., extent A, extent B, and extent C. To release space, theSRM 312 can demote the cold or low priority extents into tier 2. Ifthere is insufficient reserve space, then the SRM 312 can attempt topromote the cold extent, i.e. extent C, to the tier 0. If there isinsufficient space on tier 0, the space reservation manager 312 can senda warning to the storage system 300. The warning can be a visual orauditory alert to the storage system 300 or a user that the migration isnot possible.

FIG. 4 illustrates a flowchart of a method 400 of migrating extents torelease reserve space on a storage system, according to variousembodiments. The method 400 can be performed by the space reservationmanager and a particular storage tier. The storage system can request tothe SRM to migrate an extent. The extent may be migrated from anywherein the storage system to the target storage tier. The SRM can furthermanage the migration of extents away from the target storage tier torelease reserve space for the extent. To accomplish this, the method 400can begin at operation 402.

In operation 402, the receiving a space reservation request by the SRMcan occur. The space reservation request is a request for an extent tobe migrated to a particular storage tier within the domain of the SRM.The extent requested in operation 402 can also be referred to as arequested extent. In various embodiments, the space reservation requestcan originate from a storage controller or another storage tier. Thespace reservation request to the SRM can also include files that arecurrently being written to the storage system from an external source,e.g., a separate disk drive or a network. The space reservation requestcan be for a particular reserve space which can be managed by the spaceSRM, according to various embodiments. In various embodiments, the spacereserve request can affect extents that originate from one storage tierand migrate to another storage tier.

The space reservation request can include information such as the numberof extents 404 requested, the target tier of the request 406, and thetarget pool ID 408 of the request. For example, a space reservationrequest can take the form: “tier_id=1, reserve_cnt=n(n>=1), pool_id=x.”

The space reservation request identifies a number of extents requested.The number of extents 404 can identify one or more extents requestedfrom the requested target tier 406. According to various embodiments,the number of extents 404 can represent a requested extent count of oneor more extents that are requested from the target tier, e.g., requestedextents. The requested extent count can be a count of all spacereserveation requests sent to a target tier within a specific timeperiod, e.g., 5 minutes. Extents part of the space reservation requestcan be of the same of different sizes. If the extent size varies in thestorage system, then the space reservation request can includeinformation that indicates the extent size. For example, the spacereservation request can include the number of extents 64 kb=20, thenumber of extents 128 kb=2.

The requested target tier 406 can be requested based on policies setforth by the storage system. For example, if the storage system needs toreduce device degradation on a faster access time tier, then the storagesystem can request to migrate a hot extent, i.e., a frequently accessedextent, to a slower access time tier. As another example, the storagesystem can select a cold extent, i.e., an infrequently accessed extent,to be migrated to a slower access time tier to improve the access timeof the faster access time tier.

The target pool identification (ID) 408 can refer to the target extentpool of the number of extents 404. An extent pool is a logical constructthat is used to manage a set of extents of the same type that areassociated with a given rank group. When an extent pool is defined, itcan be assigned a rank group and an extent type. One or more ranks withthe same extent type can be assigned to an extent pool, but a rank canbe assigned to only one extent pool. There can be as many extent poolsas there are ranks. There are no constraints on the number or size ofranks assigned to the extent pool. The extents of the ranks assigned toan extent pool are independently available for allocation to logicalvolumes that are associated with the extent pool. In variousembodiments, each extent from a plurality of extents requested 404 canrequest different target extent pools. The plurality of extentsrequested 404 in the space reservation request can also be requested toa single target extent pool ID 408. For example, the space reservationrequest from a requester can inform the space reservation manager thatthe requester needs to reserve five free extents on tier 1 of Pool 2.The space reservation manager can add the count of five into the extentcount, e.g., 404, for tier 1 of pool 2. The space reservation requestcan represent a number of extents or a free value for size, according tovarious embodiments. Once the space reservation request is received,then the method 400 can continue to operation 410.

In operation 410, the SRM can determine if there is sufficient reservespace on the target tier to accommodate the migration. Although the termreserve space is used, the reserve space can be used interchangeablywith available space and accessible space throughout this disclosure. Invarious embodiments, the storage controller can determine if there issufficient reserve space to accommodate the migration to the reservespace on the target tier. For example, if the space reservation requestis larger than the reserve space on the target tier, then the reservespace on the target tier can be considered sufficient. The SRM can usethe number of extents or a file size requirement for the migration.

A requested extent can be an extent that is requested to be used by theSRM. The requested extent can be on the target tier. An available extentcan be an extent that is available to the requested extent formigration. The term sufficient reserve space can refer to the comparisonof the count of the requested extents from the space request to areserved extent count of one or more reserved extents from the reservedspace on the target tier. If there is sufficient reserve space, then themethod 400 can continue to operation 412. In operation 412, the extentsare migrated to the reserve space on the target tier or target storagetier.

If there is not sufficient reserve space, then the SRM can determinethat there is an insufficient reserve space on the target tier. Aninsufficient amount of reserve space can be determined based on a count.For example, if the count of reserved extents on the target storage tieris less than the count for requested extents, then there would be aninsufficient amount of reserve space. In various embodiments, the sizeof the extents may not be even. In this circumstance, an insufficientamount of reserve space can be determined by file size. For example, ifthere are 2 68 kb requested extents and 1 128 kb request extent, and thereserve space has enough space for 3 68 kb extents, i.e., 204 kb, thenthe SRM can determine that there is insufficient reserve space. If thereis not sufficient reserve space on the target tier, then the method 400can continue to operation 416.

In operation 416, the SRM can release reserve space on the target tier.In various embodiments, the release of reserve space can be accomplishedby migrating cold or low priority extents away from the target tier toaccommodate the space request. The migrating cold or low priorityextents can be referred to as migrating extents. The reserve space canbe released by migrating low priority extents to either a higher tierthan the target tier or a lower tier than the target tier. More reservespace can be created by the migration of low priority extents away fromthe target tier. The SRM can fill the reserve space released to the SRMwith the requested extents from the space migration request. In variousembodiments, the SRM can release a certain number or a count of reservespaces by migrating the number of extents away

A determination of whether to first migrate the low priority extent onthe target tier to the higher tier or the lower tier can occur dependingon system policy. For example, if the system policy prefers higherperformance over device stability, then the SRM can attempt to migratethe low priority extent to the lower tier before the SRM migrates thelow priority extent to the higher tier. In another example, the systempolicy can prefer device stability and first attempt to migrate the lowpriority tier to the higher tier. In various embodiments, the SRM canrelease more reserve space than the space reservation request. Thedegree to which more reserve space is released can depend upon thesystem policy.

In various embodiments, the target tier can be referred to as a firststorage tier, and the lower or higher tier can be referred to as asecond storage tier, depending on the system policy. The third storagetier can refer to destinations that extents on the second storage tiermigrate, if applicable. Throughout this disclosure, tier and storagetier may be used interchangeably.

In various embodiments, the requested extents can originate from thesecond storage tier to exchange with migrating extents on the firststorage tier. If the first storage tier has a higher performance thanthe second storage tier, then the requested extents could require fewerstorage resources than the migrating extents. The fewer storageresources can refer to the requested extent being a colder extent thanthe migrating extent, which could allow the first storage tier to be“cooled” by the colder requested extent. Thus, the storage resource canrefer to an access resource. The storage resource can also refer to astorage capacity of the extent on a storage device, according to variousembodiments.

FIG. 5 illustrates a flow chart of a method 500 to release reserve spaceon a target tier, according to various embodiments. The method 500 cancorrespond to operation 416 of FIG. 4. The method 500 can be performedby the space reservation manager. The method 500 can begin at operation518.

In operation 518, the SRM can determine the amount of deficient space,or space deficiency, on the target tier. The space deficiency can be anamount of reserve space required on the space reserve request beyond thereserve space availability of the target tier. In various embodiments,the SRM can determine the amount of reserve space by which the targettier is deficient. For example, if 500 megabytes (MB) of reserve spaceis requested in the space migration request, but the target tier onlyhas 300 MB of reserve space, then the target tier is the differencebetween the space migration request and the reserve space, and thus hasa space deficiency of 200 MB. The SRM can find a solution that enablesthe target tier to release 200 MB of reserve space.

In various embodiments, the space deficiency can be determined by acount of extents. The count can be derived from the number of extents onthe storage tier. For example, if there are 300 avaliable extents on astorage tier and there are 400 requested extents for the storage tier,then the space deficiency can be 100 extents. Therefore, the SRM wouldneed to release 100 extents worth of data. In various embodiments, theextents are the same data size or size. The extents can also be ofdifferent sizes. Once the space deficiency on the target tier isdetermined, then the method 500 can continue to operation 520.

In operation 520, the prioritization manager can prioritize the extentson the target tier. In various embodiments, the prioritizing the extentscan be based on a storage system policy. The storage system policy cantake steps to determine to prioritize performance, capacity, security,durability, or other factors. For example, if the extents areprioritized based on performance, then the most frequently accessedextents will have the highest priority since a movement of a frequentlyaccessed extent between tiers will have more of an impact on theperformance. The extents can also be prioritized based on the datacontent. For example, secure data such as financial records may have ahigh priority for movement to tiers with encryption. In variousembodiments, the extents can be ranked relative to each other in orderof priority. Further examples of prioritization are described herein.After the extents are prioritized, then the method 500 can continue tooperation 522.

In operation 522, the SRM can select the low priority extent from theprioritized list of extents determined from operation 520. The lowpriority extent may be the lowest ranked extent or the low priorityextent may be of a lower priority than the highest priority extent. Invarious embodiments, the low priority extent can be determined by athreshold. For example, the low priority extent may have a performancethreshold that does not allow the low priority extent to be selectedunless the low priority extent has an access time below a certainthreshold value.

In various embodiments, the SRM can also determine whether the lowpriority extent migration will produce enough reserve space on thetarget tier. For example, the low priority extent may be smaller thanthe space deficiency. Therefore, if the low priority extent is 150 MBbut the deficiency on the target tier is 200 MB, then an insufficientamount of reserve space will be released by the migration of the lowpriority tier. The SRM can also select more than one low priority extentto release the reserve space necessary on the target tier, including ifthe total space required of the low priority extents is larger than thespace deficiency in the target tier. After the low priority extent isselected, then the method 500 can continue to operation 524.

In operation 524, the SRM can determine whether a tier lower than thetarget tier, i.e., the lower tier is able to release the determinedamount of the space deficiency for the low priority tier. For example,if the target tier is deficient by 200 MB, and the low priority extentis 200 MB, then the SRM can determine if the tier lower than the targettier, i.e., the lower tier, has 200 MB. If the lower tier has reservespace on the lower tier greater to or equal to the space deficiency,then the method 500 can continue to operation 526. If the lower tierdoes not have enough determined reserve space on the lower tier, or thelower tier does not exist, e.g., because the target tier is the lowesttier, then the method 500 can continue to operation 528.

In operation 526, the low priority extent from the target tier can bemigrated from the target tier to the lower tier. The migration can makereserve space accessible on the target tier for the space request inFIG. 4.

In operation 528, the SRM can determine whether reserve space can bereleased on the lower tier sufficient for the target tier low prioritytier. Reserve space can be released if one or more extents on the lowertier can be migrated to a different tier. In various embodiments, theSRM can predict whether space can be released using simulated data. Forexample, if 200 MB is needed on the lower tier, and the lower tier canmigrate an extent to a first tier to free 200 MB, then reserve space canbe released. It can also be possible for the operation to occur in acascading fashion if not enough reserve space exists on the first tier.For example, if the first tier does not have 200 MB reserve space, thenthe first tier can migrate first tier extents to another tier to releasethe space. If the SRM is able to release the reserve space on the lowertier, then the method 500 can continue to operation 530. If SRM is notable to release reserve space on the lower tier, then the method 500 cancontinue to reference A.

In operation 530, the SRM can release reserve space on the lower tier inorder to accept a migration from the target tier. The SRM can executethe simulation paths determined in operation 528. In variousembodiments, the release of reserve space can involve a swap. A swapcould migrate a low priority extent from the lower tier to the targettier and migrate a high priority extent from the target tier to thelower tier. A swap could generate more reserve space on the target tierif the low priority extent is smaller than the high priority extentmigrated. The swap can require a buffer area for the lower tier toaccept the high priority extent. After the reserve space is released onthe lower tier, the method 500 can continue to operation 526 where thelow priority extent from the target tier is migrated to the lower tier.

FIG. 6 illustrates a flowchart of a method 600 of migrating a lowpriority extent to a higher-level tier than the target tier, accordingto various embodiments. The method 600 can continue from reference A onFIG. 5 or stand independent. Certain operations of the method 600 can besimilar in operation to method 500 in FIG. 5. For example, operation 628can be similar to the analysis used for operation 528 in FIG. 5. Themethod 600 can correspond to a portion of operation 416 from FIG. 4. Invarious embodiments, aspects of method 600 can occur before aspects usedin FIG. 5. For example, the method 600 can be inserted between operation522 and 524 of FIG. 5. The method 600 can begin at operation 624.

In operation 624, the SRM can determine if the deficient amount ofreserve space, or space deficiency, from the target tier exists on thetier with a higher priority than the target tier, e.g., the higher tier.The higher tier can be marked by a shorter access time such as an SSD.In various embodiments, the target tier may not have a higher tier orthere is not enough reserve space on the higher tier and the method 600can continue to operation 628. If the higher tier contains enoughcapacity to accommodate the low priority extent from the target tier,then the method 600 can continue to operation 626.

In operation 626, the SRM can migrate the low priority extent from thetarget tier to the higher tier. By this migration, the SRM can alsoreduce a load on the higher tier by inserting a lower priority extent,or cold extent. In operation 628, the SRM can determine if reserve spacecan be released on the higher tier by migrating one or more extents awayfrom the higher tier to a different tier. If reserve space cannot bereleased on the higher tier, then the method 600 can continue tooperation 636. If reserve space can be released on the higher tier, thenthe SRM can release the reserve space on the higher tier in operation630. After the reserve space is released on the higher tier, then themethod 600 can continue to operation 626.

In operation 636, the SRM can notify the storage system of the inabilityto accept the space request. It may be possible for the target tier tonot be able to release reserve space by migrating a low priority extentto a higher or lower tier. If this occurs, then the storage systemcannot accept the space request, e.g., operation 402 in FIG. 4. The SRMcan also notify the storage system such as a visual communication or apop up window to indicate that the migration is not possible. After thenotification in operation 636, the method 600 may halt.

FIG. 7 illustrates a block diagram of a prioritization system 700 thatcan be used in the prioritization module, according to variousembodiments. The prioritization system 700 can be for prioritizing aplurality of extents within the same rank. For example, in a 2-tierpool, Tier 0 and Tier 1, Tier 0 may have one SSD rank and Tier 1 mayhave three ENT ranks, e.g., ENT rank A, ENT rank B, and ENT rank C. Ifthe SRM needs to release reserve space in Tier 1, then the SRM may needto select a particular rank within Tier 1. The selection of the rankwithin Tier 1 can occur randomly, in various embodiments. For example,the prioritization system 700 can select ENT rank B randomly.

Once selected, the prioritization system 700 can further divide the ENTrank A into twelve “buckets” or containers. Although 12 buckets areshown, i.e., bucket 0 through bucket 11, more or fewer buckets arecontemplated.

The prioritization system 700 can create the buckets according to ameasurement of the extent's respective Exponential Moving Average (EMA)I/O operations per second (IOPS). The EMA is an average value based onlong-term performance statistics. The measurement can occur using avariety of techniques. For each rank candidate of Space Reservation, itsextents are divided into different buckets. Extents in bucket 11 canhave the largest IOPS, and those in bucket 1 can have the smallest IOPS.Bucket 0 can include a buffer for extents which have just been moved andshould stay there for a minimum time range.

In each of the buckets, e.g., bucket 1, the extents are sorted accordingto the ascending order of instant IOPS. The instant IOPS differs fromthe EMA IOPS in that the instant IOPS refers to a real-time value. Theprioritization module can select the coldest extent from bucket 1 untilbucket 11, e.g, extent 0 until no more extents are required in theprioritization module. The coldest extent can mean that the extent hasthe smallest instant IOPS.

FIG. 8 depicts a block diagram of automated computing machinery,according to an embodiment. The computing machinery can include examplecomputer 852 useful in performing aspects of the disclosure, accordingto various embodiments. The computer 852 of FIG. 8 includes at least onecomputer processor 856 or ‘CPU’ as well as random access memory 868('RAM') which is connected through bus adapter 858 to processor 856 andto other components of the computer 852.

Also stored in RAM 868 is an operating system 854. Operating systemsuseful for record filtering according to embodiments of the presentinvention include UNIX®, Linux®, Microsoft XP™, AIX®, IBM's i5/OS™, andothers. The operating system 854 and simulator 801 are shown in RAM(868), but many components of such software typically are stored innon-volatile memory also, such as, for example, on a disk drive 870.

The computer 852 can also include disk drive adapter 872 coupled throughexpansion bus 860 and bus adapter 858 to processor 856 and othercomponents of the computer 852. Disk drive adapter 872 connectsnon-volatile data storage to the computer 852 in the form of disk drive870. Disk drive adapters useful in computers include Integrated DriveElectronics ('IDE') adapters, Small Computer System Interface ('SCSI')adapters, and others. Non-volatile computer memory also may beimplemented for as an optical disk drive, electrically erasableprogrammable read-only memory (so-called ‘EEPROM’ or ‘Flash’ memory),RAM drives, and so on.

The disk drive 870 can have a storage controller 802. The storagecontroller 802for the disk drive 870 can have a prioritization module822 and a space reservation manager module 834. The prioritizationmodule 822 can prioritize the extents on a tier in the disk drive 870.The prioritization module 822 can communicate the priority to the SRMmodule 834. The storage controller 802 can also have an SRM module 834which can migrate the extents within the disk drive 870.

The example computer 852 includes one or more input/output (‘I/O’)adapters 878. I/O adapters implement user-oriented input/output through,for example, software drivers and computer hardware for controllingoutput to display devices such as computer display screens, as well asuser input from user input devices 881 such as keyboards and mice. Theexample computer 852 includes a video adapter 809, which is an exampleof an I/O adapter specially designed for graphic output to a displaydevice 880 such as a display screen or computer monitor. Video adapter809 is connected to processor 856 through a high speed video bus 864,bus adapter 858, and the front side bus 862, which is also a high speedbus.

The example computer 852 includes a communications adapter 867 for datacommunications with other computers 810, e.g., mobile devices, and fordata communications with a data communications network 800. Such datacommunications may be carried out serially through RS-232 connections,through external buses such as a Universal Serial Bus (‘USB’), throughdata communications networks such as IP data communications networks,and in other ways as will occur to those of skill in the art.Communications adapters implement the hardware level of datacommunications through which one computer sends data communications toanother computer, directly or through a data communications network.Examples of communications adapters include modems for wired dial-upcommunications, Ethernet (IEEE 802.3) adapters for wired datacommunications network communications, and IEEE 802.77 adapters forwireless data communications network communications.

The descriptions of the various embodiments of the present disclosurehave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

Referring to FIG. 8, the present invention may be a system, a method,and/or a computer program product. The computer program product mayinclude a computer readable storage medium (or media) having computerreadable program instructions thereon for causing a processor to carryout aspects of the present invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Java, Smalltalk, C++ or the like,and conventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

What is claimed is:
 1. A method, comprising: receiving a spacereservation request for one or more requested extents on a first storagetier of a storage system; releasing a first storage tier reserve spacethat includes one or more first tier reserved extents in response to thefirst storage tier reserve space being insufficient for the reservationrequest by: prioritizing a plurality of first tier extents on the firststorage tier, determining a space deficiency for the space reservationrequest in the first storage tier, selecting one or more migratingextents on the first storage tier that are at least equal to the spacedeficiency, and migrating the one or more migrating extents to a secondstorage tier in response to the second storage tier having a secondstorage tier reserve space for the one or more migrating extents; andmigrating the one or more requested extents to the first storage tierreserve space.
 2. The method of claim 1, further comprising: migrating,in response to the space reservation request being sufficient for thefirst storage tier reserve space, the one or more requested extents tothe first storage tier.
 3. The method of claim 1, wherein the receivingthe space reservation request includes: receiving a target storage tierthat identifies the first storage tier, a requested extent count derivedfrom the one or more requested extents on the first storage tier, and apool identification for the first storage tier.
 4. The method of claim3, wherein determining the space deficiency includes determining adifference between a requested extent count from the one or morerequested extents and a first tier reserved extent count from the one ormore first tier reserved extents.
 5. The method of claim 1, whereinreleasing the first storage tier reserve space further comprises:determining whether a third storage tier reserve space can be releasedin response to the second storage tier not having a second storage tierreserve space for the one or more migrating extents from the firststorage tier; and migrating one or more migrating extents from thesecond storage tier to the third storage tier.
 6. The method of claim 5,wherein determining whether the third storage tier reserve space can bereleased comprises: determining a second tier space deficiency, whereinthe second tier space deficiency is a difference between the secondstorage tier reserve space and the one or more migrating extents fromthe first storage tier; prioritizing a plurality of extents on thesecond storage tier; and selecting one or more migrating extents on thesecond storage tier at least equal to the second storage tier spacedeficiency.
 7. The method of claim 1, wherein the migrating extent is alow priority extent.
 8. The method of claim 1, wherein prioritizing theplurality of extents on the first storage tier includes: selecting arank from a plurality of ranks within the first storage tier; measuring,for the rank, an Exponential Moving Average (EMA) I/O Operations perSecond (IOPS) for a plurality of containers; prioritizing the pluralityof containers by the EMA IOPS; prioritizing the plurality of extentswithin a container based on a measurement of an IOPS for an extent; andselecting a lowest priority extent within a container from the pluralityof containers.
 9. The method of claim 8, wherein selecting the rank fromthe plurality of ranks occurs randomly.
 10. The method of claim 1,wherein the second storage tier has a higher relative performance thanthe first storage tier.
 11. The method of claim 1, wherein at least onerequested extent from the one or more requested extents has a differentdata size than another requested extent.
 12. The method of claim 1,wherein the one or more requested extents originate from the secondstorage tier.
 13. The method of claim 12, wherein the one or morerequested extents use fewer storage resources than the one or moremigrating extents.
 14. A system, comprising: a plurality of storagetiers on one or more storage devices with at least one high performancestorage tier relative to the plurality of storage tiers, wherein a firststorage tier from the plurality of storage tiers has one or moreavailable extents; a prioritization module configured to determine apriority of an extent on the plurality of storage tiers and communicatethe priority to a space reservation manager; the space reservationmanager configured to: receive a space reservation request for amigration of one or more requested extents to the first storage tier,release, in response to one or more available extents on the firststorage tier being insufficient for the space reservation request, areserve space on the first storage tier by: receiving the priority of aplurality of extents on the first storage tier from the prioritizationmodule, determining a space deficiency between the one or more requestedextents for the space reservation request and the one or more availableextents in the first storage tier, selecting one or more migratingextents from the plurality of extents on the first storage tier at leastequal to the space deficiency, and migrating the one or more migratingextents to a second storage tier in response to the second storage tierhaving sufficient space for the one or more migrating extents; andmigrate the one or more requested extents to the reserve space on thefirst storage tier.
 15. The system of claim 14, wherein the spacereservation manager is configured to select one or more migratingextents by selecting a low priority extent from the plurality of extentswith a determined priority
 16. The system of claim 14, wherein the spacereservation manager is configured to receive the space reservationrequest including: a target storage tier that identifies the firststorage tier, a count derived from the one or more requested extents onthe first storage tier, and a pool identification for the first storagetier.
 17. The system of claim 16, wherein the space reservation manageris configured to determine the space deficiency by: determining adifference between the count of the one or more requested extents and acount of the one or more available extents.
 18. A computer programproduct for managing one or more extents within storage devices, thecomputer program product comprising a computer readable storage mediumhaving program code embodied therewith, the program code comprisingcomputer readable program code configured to: receive a spacereservation request for one or more requested extents on a first storagetier of a storage system; release, in response to one or more availableextents on the first storage tier being insufficient for the spacereservation request, a first storage tier reserve space by: prioritizinga plurality of extents on the first storage tier, determining a spacedeficiency between the one or more requested extents for the spacereservation request and the one or more available extents in the firststorage tier, selecting one or more migrating extents from the pluralityof extents on the first storage tier that are at least equal to thespace deficiency, and migrating the one or more migrating extents to asecond storage tier in response to the second storage tier having asecond storage tier reserve space for the one or more migrating extents;and migrate the one or more requested extents to the first storage tierreserve space.
 19. The computer program product of claim 18, wherein thecomputer readable computer code is configured to release the firststorage tier reserve space by: determining whether a third storage tierreserve space can be released in response to the second storage tier nothaving a second storage tier reserve space for the one or more lowpriority extents from the first storage tier; and migrating one or morelow priority extents from the second storage tier to the third storagetier.
 20. The computer program product of claim 19, wherein the computerreadable computer code is configured to determine whether the thirdstorage tier reserve space can be released comprises: determining asecond tier space deficiency, wherein the second tier space deficiencyis a difference between the second storage tier reserve space and theone or more low priority extents from the first storage tier;prioritizing a plurality of extents on the second storage tier; andselecting one or more migrating extents on the second storage tier atleast equal to the second storage tier space deficiency.